Suppression of Ru (S = 1) spin dimerization in La2RuO5 by Ti substitution

Abstract

La2RuO5 shows a magneto-structural phase transition at 161 K with spin dimerization and concomitant formation of a non-magnetic singlet ground state. To gain a deeper insight into the origin of this transition systematic substitution of Ru by Ti has been carried out. Polycrystalline samples have been synthesized by thermal decomposition of citrate precursors leading to La2Ru1−yTiyO5 (0 ≤ y ≤ 0.45). The crystal structure was investigated by x-ray powder diffraction at room temperature and at 100 K. The valences of Ti and Ru were obtained from x-ray absorption near edge structure spectroscopy at the Ti–K and the Ru–LIII absorption edges, respectively. The magnetic phase transition was investigated by magnetic susceptibility measurements as a function of Ti substitution, revealing a decreasing transition temperature on increasing the level of substitution. The step-like feature in the magnetic susceptibility reflecting the Ru–Ru spin dimerization transition becomes smeared out close to y = 0.3 and completely vanishes at y = 0.45, indicating complete suppression of spin-dimer formation. Additional specific-heat measurements show a continuous decrease of the magnetic entropy peak with increasing Ti substitution mirroring the reduced number of spin dimers due to the magnetic dilution. A magnetic anomaly of the dimerization transition can hardly be detected for y ≥ 0.3. Density functional theory calculations were carried out to study changes of the electronic band structure caused by the substitution. A possibly preferred distribution of Ti and Ru and the magnetic interactions as well as the change of the density of states close to the Fermi level are investigated. Based on these experimental results a detailed (y,T) phase diagram is proposed.